This project is designed to study two particular aspects of copper rich dental amalgams. The microstructures of 13 commercial systems have been qualitatively compared with each other and with a conventional amalgam system. The major difference is the replacement of most of the weak, corrosion prone gamma 2 (Sn-Hg) phase with Cu6 Sn5. The initial formation of the gamma 2 phase and its subsequent disappearance and the relative growth of the Cu6 Sn5 phase have been studied by X-ray diffraction. An attempt will be made to determine the quantities of each phase present as a function of time. Major corrosion products on conventional amalgams have been identified as Sn4(OH)6Cl2 and SnO. Products are being grown in chloride and sulfide solutions on the copper rich amalgams and will be compared with those from the conventional amalgams. This comparison is done by scanning electron microscopy, energy dispersive X-ray analyses, and X-ray diffraction for morphology, chemical composition and comparison with d-spacings of known compounds.